Coalescence and Phase Separation During Spinodal Decomposition of Solvent Mixtures Far From the Critical Point

摘要-9978781 R。MauriCUNY City College在这项工作的前几个阶段，我们已经研究了当部分互溶液体的混合物在其溶解度曲线上深度淬火时发生的相变[2][4]。这项研究的动机是以前的NSF资助的调查，其中溶剂[1][3]。这项工作的主要结果之一是发现，在相变之后，聚结和相分离非常迅速，即使当乳化剂和表面活性化合物溶解在混合物中时也是如此。与大多数输运过程一样，相分离由两个基本的去雾过程驱动，通过使用高粘度体系，如聚合物熔体和合金，或通过使液体混合物仅在其溶解度曲线以下几个毫开尔文淬灭[6]-[9]。在这些情况下，在系统的温度刚刚越过溶解度曲线的温度之后，混合物相通过形成明确定义的斑块而分离，其典型尺寸随时间增长为t1/3 [6]-[10]。另一方面，低粘度、深度骤冷的液体混合物由于吸引力的影响而通过对流分离，这往往使界面面积最小化。在我们最近对旋节分解的研究中，我们发现对流导致了快速聚结液滴的信息，其典型尺寸随时间线性增长。此外，我们的研究结果表明，表面张力驱动的吸引力远大于排斥静电力，从而解释了为什么低粘度液体混合物的相分离迅速发生，而不管乳化剂的存在。需要做大量的工作来实现我们的最终目标，并对在表面活性化合物存在下的相变期间液体混合物的流动进行建模。以下建议旨在解决其中一些问题。特别是，我们希望集中在以下四个领域的研究。1.部分互溶液体混合物相分离和旋节线分解过程中形成乳状液和阻碍聚结的化合物和杂质的作用。正如我们所看到的，在萃取过程中使用部分混溶溶剂的主要优点之一是相分离不受乳化剂存在的影响。在这项研究中，我们打算更好地理解这种现象，强调这种现象不再发生的局限性。2.粘度在相分离过程中的作用。由于我们知道低粘度流体混合物（Peclet数大于10，000）中的相分离与高粘度流体混合物（Peclet数小于10）中的相分离非常不同，因此我们建议研究具有中等粘度的宏观静止相分离液体混合物的动力学，即Peclet数范围为10至10，000.3。剪切对旋节线分解的作用。这项研究的动机是，在实际的提取过程中，快速冷却需要混合，这反过来又可能导致乳化。这个过程可以在Couette装置中模拟，其中流体混合物经历恒定的剪切。4.扩展我们的理论模型，以模拟前面3点中研究的效果。

ABSTRACTCTS-9978781R. MauriCUNY City CollegeIn the previous stages of this work we have studied the phase transition occurring when a mixture of partially miscible liquids is deeply quenched across its miscibility curve [2][4]. This study was motivated by a previous NSF-funded investigation, where solvents [1][3]. One of the main results of this work was the discovery that, following phase transition, coalescence and phase segregation are very rapid, even when emulsifiers and surface-active compounds are dissolved within the mixture.Like most transport processes, phase separation is driven by two basic demising process is retarded by either using high-viscosity systems, such as polymer melts and alloys, or by quenching the liquid mixtures only by few millikelvins below their miscibility curve [6]-[9]. In these cases, right after the temperature of the system has crossed that of the miscibility curve, the mixture phase separates by forming well-defined patches, whose typical size grows wit time as t1/3 [6]-[10]. On the other hand, low-viscosity, deeply quenched liquid mixtures separates by convection, due to the influence of an attractive force, which tends to minimize the interfacial area. In our recent studies on spinodal decomposition, we showed that convection leads to the information of rapidly coalescing drops, whose typical size grows linearly in time. In addition, our results have shown that surface tension-driven attractive forces are far larger that repulsive electrostatic forces, thus explaining why the phase separation of low-viscosity liquid mixtures occurs rapidly, irrespectively of the presence of emulsifiers.While our investigation has produced novel and unexpected results, much work is required to achieve our ultimate goal and model the flow of liquid mixtures during phase transition in the presence of surface-active compounds. The following proposal is intended to address some of these problems. In particular, we want to focus on the following four areas of research.1. The role of emulsion-forming and coalescence-hindering compounds and impurities during phase segregation and spinodal decomposition of partially miscible liquid mixtures. As we saw, one of the main advantages of using partially miscible solvents in extraction processes is that phase segregation is unaffected by the presence of emulsifiers. In this research we intend to better understand this phenomenon, stressing the limitations under which is ceases to occur.2. The role of viscosity during phase separation. Since we know that phase separation in low-viscosity fluid mixtures (with Peclet numbers larger than 10,000) is very different than in high-viscosity's (with Peclet numbers smaller than 10), we propose to study the dynamics of macroscopically quiescent phase separating liquid mixtures with intermediate viscosity, i.e. with Peclet numbers ranging from 10 to 10,000.3. The role of shear on spinodal decomposition. This investigation is motivated by the fact that in practical extraction processes a rapid cooling requires mixing, which in turn may cause emulsification. This process can be modeled in a Couette apparatus, where the fluid mixture undergoes constant shear.4. Extension of our theoretical model to simulate the effects studied in the previous 3 points.